This invention relates to amplitude equalization circuits and in particular to amplitude equalization circuits used on transmission lines.
There are several examples of equalization circuits known in the art such as those provided in Landee, Robert W., Davis, Donovan C., and Albrecht, Albert P., Electronic Designers' Handbook, McGraw-Hill, 1957, pp. 17-4-17-15, which disclose non variable equalizers that are used only where deviations are known and predictable and are not long-term time variants. An example of variable equalization circuits is disclosed in Bode, H. W., "Variable Equalizers," Bell System Technical Journal, Vol. 17, pp. 229-244, April, 1938, which were truly variable equalization circuits with positive and negative equalization. The Bode circuits required inverse networks in at least two branches which must be accurately matched against each other and required at least two inductor/capacitor resonators. Furthermore, at least one branch must not be connected to the reference potential or ground.
Since the advent of modern semiconductor technology many advances have been achieved in the design of equalization circuits such as the octave equalization circuits disclosed to the National Semiconductor Audio Handbook, Section 2.17, which are limited to fairly low values of bandwidth ratio.
In U.S. Pat. No. 3,646,464 an adjustable active delay amplitude circuit including operational amplifier and resistive and reactive circuit elements in which the adjustment for amplitude can be made substantially independent of an adjustment for delay was disclosed. This circuit required that a differential amplifier must be used and that the inductor cannot be connected to ground. The circuitry had associated with it a zero to 180.degree. phase shift, and restrictions on the slops of the curve that is to be equalized.
The frequency response of the frequency sensitive amplitude equalization circuit disclosed herein can be adjusted by a single potentiometer to be either flat or give a positive or negative gain at a selected frequency.
The disclosed circuit uses only one grounded inductor which can be realized by an inductor or a variety of simple active circuits whose response represents that of a physical inductor. The magnitude and shape of the resulting frequency response is determined by series resistive elements and the ratio of the inductance to capacitance. The bandwidth of the disclosed circuit is limited only by the quality of the inductor, or active circuit with the response of an inductor, used. In addition the circuit requires only an inverting amplifier which provides in combination with the other elements a minimized relative phase shift in the order of 180.degree. plus or minus 90.degree.. There are no restrictions placed on the shape of the curve to be equalized. In fact, a very complex shape which varies only in magnitude can be equalized with one control element. Several equalization circuits may be ganged together to provide either a positive or negative gain bump over a wide band of frequencies and in one circuit disclosed herein it has been used to provide a linear response over a wide band of frequencies.
Many advantages of the present invention may be ascertained from a reading of the specification and the claims in conjunction with the drawings.